242 ROLE OF CYTOPLASM [CH. 



incompatibility of the parental chromosomes, as in FEDER- 

 LEY'S Pygaeras. The hypothesis must therefore remain little 

 more than a speculation until both the genetic and cyto- 

 logical facts are better known. GOLDSCHMIDT'S idea of a 

 female determining factor borne by the cytoplasm in Lepi- 

 doptera might be quoted in support of this hypothesis. 



Another argument that has been adduced in favour of 

 the importance of the cytoplasm, or at least against the 

 exclusive role of the chromosomes, in heredity, is that crosses 

 between distantly related forms may give offspring of the 

 pure maternal type. A well-known instance of this is pro- 

 vided by GODLEWSKI'S experiment of fertilising the eggs of 

 Echinus with sperm of the Crinoid Antedon, by which he got 

 pluteus larvae showing no trace of Crinoid characters. He 

 also fertilised non-nucleated fragments of Echinus eggs with 

 Antedon sperm, and obtained blastulae and a few gastrulae 

 of the Echinoid type, though these never developed any 

 skeletal structures. Since the Antedon chromosomes were 

 not extruded, but apparently behaved normally in the 

 segmentation divisions, this experiment has often been used 

 as an argument that the chromosomes do not determine 

 inherited characters, or at least those characters which dis- 

 tinguish one Order from another. Similar results have been 

 observed (for example by LOEB) in crosses between Sea- 

 urchins and Starfish and by PINNEY in Teleostean hybrids. 

 As was mentioned in Chapter IX, however, it is known that 

 the entrance of a spermatozoon may stimulate an egg to de- 

 velop even though the sperm-nucleus takes no part in the 

 cell-divisions, as happens when Sea-urchin eggs are fertilised 

 with Mytilus sperm, and there seems to be no sufficient 

 reason against regarding these purely maternal "hybrids" 

 as something of the same sort. It may be supposed, for 

 example, that when forms are crossed in which there is a 



